Synthetic, Structural, and Spectroscopic Studies of Sterically Crowded Tin–Chalcogen Acenaphthenes

A series of sterically encumbered <i>peri</i>-substituted acenaphthenes have been prepared containing chalcogen and tin moieties at the close 5,6-positions (Acenap­[SnPh₃]­[ER], Acenap = acenaphthene-5,6-diyl, ER = SPh (<b>1</b>), SePh (<b>2</b>), TePh (<b>3</b>), SEt (<b>4</b>); Acenap­[SnPh₂Cl]­[EPh], E = S (<b>5</b>), Se (<b>6</b>); Acenap­[SnBu₂Cl]­[ER], ER = SPh­(<b>7</b>), SePh (<b>8</b>), SEt (<b>9</b>)). Two geminally bis­(<i>peri</i>-substituted) derivatives ({Acenap­[SPh₂]}₂SnX₂, X = Cl (<b>10</b>), Ph (<b>11</b>)) have also been prepared, along with the bromo–sulfur derivative Acenap­(Br)­(SEt) (<b>15</b>). All 11 chalcogen–tin compounds align a Sn–C_Ph/Sn–Cl bond along the mean acenaphthene plane and position a chalcogen lone pair in close proximity to the electropositive tin center, promoting the formation of a weakly attractive intramolecular donor–acceptor E···Sn–C_Ph/E···Sn–Cl 3c-4e type interaction. The extent of E→Sn bonding was investigated by X-ray crystallography and solution-state NMR and was found to be more prevalent in triorganotin chlorides <b>5</b>–<b>9</b> in comparison with triphenyltin derivatives <b>1</b>–<b>4</b>. The increased Lewis acidity of the tin center resulting from coordination of a highly electronegative chlorine atom was found to greatly enhance the lp­(E)−σ*­(Sn–Y) donor–acceptor 3c-4e type interaction, with substantially shorter E–Sn <i>peri</i> distances observed in the solid state for triorganotin chlorides <b>5</b>–<b>9</b> (∼75% ∑<i>r</i>_vdW) and significant ¹<i>J</i>(¹¹⁹Sn,⁷⁷Se) spin–spin coupling constants (SSCCs) observed for <b>6</b> (163 Hz) and <b>8</b> (143 Hz) in comparison to that for the triphenyltin derivative <b>2</b> (68 Hz). Similar observations were observed for geminally bis­(<i>peri</i>-substituted) derivatives <b>10</b> and <b>11